Hi dschaal, Thank you for your question. I understand that Firefox is the only browser that gives you this error when you try to login to your webmail. So far there has not been alot of questions from Firefox users on Windows 10, so we may be a bit in the dark here.

However the error message should also give a hint to what might be happening, most of the time. This is an SMTP error message. Do you have the full HTTP header error message? You can compare this to the one in the other browser to get an idea of what might be blocking this.

I can hypothesize a port a blocked, or there is a security certificate that might be blocking the login. If it was a one time occurrence it is also possible to delete the cookies from the site in Firefox to make sure its just not a corrupt cookie. Clear cookies and site data in Firefox

Clear the cache and remove cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

If you use extensions (Firefox/Tools > Add-ons > Extensions) that can block content (e.g. Adblock Plus, NoScript, Flash Block, Ghostery) then make sure that such extensions aren't blocking content.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes